## Support semantics
This is a **candidate / unverified** Solution from the KFA Solution Factory Tier-2 gate. It is source-grounded research material, not an Outcome, and does **not** claim independent reproduction or confirmed field success.
## Cause
The specification retired -32042 when URL elicitation moved from a JSON-RPC error response to MRTR input_required results with elicitation/create requests on 2026-07-28.
## Steps
1. Record the negotiated protocol era after connect (2025-11-25 vs 2026-07-28).
2. On 2025-11-25: register a handler for JSON-RPC error -32042; open each URL-mode elicitation from error.data.elicitations after user consent, then retry the original request.
3. On 2026-07-28: handle tools/call (and other MRTR-capable methods) returning resultType input_required; process inputRequests such as elicitation/create instead of polling for -32042.
4. Do not emit -32042 from 2026-07-28 servers; clients must not treat reserved legacy codes as active signals on modern connections.
## Expected result
URL authorization flows complete on both eras: legacy clients react to -32042; 2026-07-28 clients complete elicitation through in-band input_required rounds without relying on a retired error code.
## Misleading approaches
- Assuming -32042 will appear on 2026-07-28 connections.
- Ignoring input_required MRTR results because the client only implements -32042 handling.
## Limitations
- Exact server era and elicitation payload shapes must be read from live negotiation and responses.
- This pass did not reproduce end-to-end OAuth flows against a live server.
## Unknowns
- Whether a given third-party server still implements 2025-11-25 error semantics vs full 2026-07-28 MRTR elicitation.
## Evidence claims
- (documented_platform_behavior) 2026-07-28 implementations MUST NOT emit error code -32042. — https://raw.githubusercontent.com/modelcontextprotocol/modelcontextprotocol/ab3a39c13bd23be691c2760e1c6c5c15a64582e1/docs/specification/2026-07-28/basic/index.mdx
- (documented_platform_behavior) 2025-11-25 defines URLElicitationRequiredError with code -32042 for required URL-mode elicitation. — https://raw.githubusercontent.com/modelcontextprotocol/modelcontextprotocol/ab3a39c13bd23be691c2760e1c6c5c15a64582e1/docs/specification/2025-11-25/client/elicitation.mdx
- (documented_platform_behavior) 2026-07-28 carries elicitation through input_required MRTR results with elicitation/create input requests rather than -32042 errors. — https://raw.githubusercontent.com/modelcontextprotocol/modelcontextprotocol/ab3a39c13bd23be691c2760e1c6c5c15a64582e1/docs/specification/2026-07-28/basic/patterns/mrtr.mdx
Proposed approach
- Problem id
- 1d1ee05a-b09b-4abe-98d1-34ee8d9655e9
- Proposed action
- Branch on negotiated protocol era: on 2025-11-25 connections, handle error code -32042 by presenting the URL elicitations in error.data and retrying after completion; on 2026-07-28 connections, never wait for -32042—parse input_required tool results and satisfy elicitation/create input requests in the MRTR flow.
- Applicability
- State
- partial
- Text
- support: candidate_unverified (not an Outcome; no reproduction claim); MCP clients integrating URL-mode OAuth, payments, or other out-of-band flows across both 2025-11-25 and 2026-07-28 servers; symptom is missing URL prompts when only -32042 is handled, or generic errors when -32042 is unknown on legacy servers.; affected: MCP spec 2025-11-25 (-32042 defined); MCP spec 2026-07-28 (-32042 reserved, must not be emitted); fix_status: CONFIRMED_SOLUTION
- Limitations
- State
- partial
- Text
- Exact server era and elicitation payload shapes must be read from live negotiation and responses. This pass did not reproduce end-to-end OAuth flows against a live server.
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
Needs revalidation
LOW EVIDENCE
This exact knowledge revision needs ordinary execution evidence.
Useful environment or version
- State
- partial
- Text
- support: candidate_unverified (not an Outcome; no reproduction claim); MCP clients integrating U
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